1. Field
This invention pertains generally to circuit interrupters and, more particularly, to a method of tripping a circuit interrupter being operated in aback fed configuration.
2. Background Information
Circuit interrupters include, for example, circuit breakers, contactors, motor starters, motor controllers, and other load controllers and receptacles having a trip mechanism. Circuit breakers are used to protect electrical circuitry from damage due to, for example, an overcurrent condition, such as an overload condition or a relatively high level short circuit or fault condition, or an arc fault or ground fault condition. A circuit breaker typically includes a pair of separable contacts per phase. The separable contacts may be operated either manually by way of a handle disposed on the outside of the circuit breaker, or automatically in response to detection of an overcurrent condition. With respect to the automatic mode of operation, the circuit breaker typically includes: (i) operating mechanism operatively coupled to an actuator, such as a solenoid, which together are designed to rapidly open and close the separable contacts, and (ii) a trip unit which senses overcurrent conditions and in response causes the actuator and operating mechanism to move the separable contacts to their open position.
Most commonly, circuit breakers are forward fed, meaning that an AC power source is connected to the line side of the circuit breaker and power is delivered to a load coupled to the load side of the circuit breaker through the separable contacts of the breaker. In such a configuration, in a fault condition, the circuit breaker measures the voltage on the load side of the separable contacts to determine when to stop firing the actuator (e.g., the solenoid). More specifically, when there is no voltage being sensed on the load side (i.e., because the separable contacts have been successfully opened), the firing of the actuator will be stopped.
It is also known to operate circuit breakers in a back fed application wherein an AC power source, such as, without limitation, a photovoltaic cell array with an inverter or DC-to-AC converter, is connected to the load side of the circuit breaker and power is delivered to the line side through the separable contacts of the breaker. In such a configuration, voltage remains on the load side of the breaker even when the breaker is in the tripped or disconnected state. This is problematic as it will cause the breaker to continue to fire the actuator (e.g., solenoid), even though the breaker is already disconnected, until the actuator fails.